1. Field of the Invention
This invention relates to a technique for fabrication of shaped parts from composite materials containing a superconductive oxide with the shaped parts having a superconducting-normal transition temperature above the liquid nitrogen boiling temperature.
2. Discussion of Background
Several compositions of superconductive powders exist in the prior art having transition temperatures above the boiling point of nitrogen.
Examples of such recent prior art are disclosed in "Superconductivity at 93K in a New Mixed-Phase Y--BA--Cu--O Compound System at Ambient Pressure", by M. K. Wu, et al, Physical Review Letters, (58) 9, Mar. 2, 1987, pp. 908. This system utilizes YBa.sub.2 Cu.sub.3 O.sub.(7-x). Other examples include R. J. Cava. et al, "Bulk Superconductivity at 91K in Single-Phase Oxygen-Deficient Perovskite Ba.sub.2 YCu.sub.3 O.sub.9-x ", Physical Review Letters, (58) 16, Apr. 20, 1987, pp. 1676, and YBa.sub.2 Cu.sub.3 F.sub.x O.sub.y, see S. R. Ovshinsky, et al, "Superconductivity at 155K", Physical Review Letters (58) 24, Jun. 15, 1987, pp. 2579.
Other similar compositions have been recently disclosed wherein Y is replaced by other Rare Earth metals as for example, P. H. Hor, et al, "Superconductivity Above 90K in the Square-Planar Compound System ABa.sub.2 Cu.sub.3 O.sub.6+x with A.dbd.Y, La, Nd, 5m, Fu, Gd, Ho, Er, and Lu", Physical Review Letters, (58) 18, May 4, 1987, pp. 1891.
The primary goal with each of these constructions is to produce shaped parts from these powders which presents tremendous difficulties pertaining to both the method of processing and the resulting properties. Typical among these problems are brittleness and low formability subsequent to sintering.
The prior art processing methods for parts which are made of 1-2-3 oxides involve traditional ceramic processing (e.g. mixing-pressing-sintering, mixing-casting-sintering), and forming superconductor wire by molten oxide processing as indicated by S. Jin et al, "Fabrication of Dense Ba.sub.2 YCu.sub.3 O.sub.7-x Superconductor Wire by Molten Oxide Processing", Applied Physics Letters 51(12), Sep. 21, 1987. Other methods involve, for example, "superconductors-composite wire fabrication, S. Jin et al, "High Tc Superconductors-Composite Wire Fabrication", Applied Physics Letters 51(3), Jul. 20, 1987, and the explosive cladding technique, Lawrence E. Murr, Alan W. Hare, Nicholas G. Eror, "Introducing: The Metal-Matrix High Temperature Superconductor", Advanced Materials & Processes', Inc., Metal Progress, October, 1987.
The numerous disadvantages of each of the above processes result from the fact that they each involve the 1-2-3 powder, which will produce a part which is both mechanically hard and very brittle. Although the superconductors-composite wire fabrication process results in better mechanical properties, it can only be utilized for the production of specialized shaped parts such as wires. On the other hand, the explosive cladding technique is a very complicated process which only allows for the production of simple shaped parts, which also have the disadvantage of non-uniform macro-structure, composed of two different materials.
Therefore, it is quite obvious that a need exists, and, in fact, an urgency exists, to produce shaped parts from higher temperature superconductive materials which overcome the disadvantages of the prior art methods of producing shaped parts.